SAR Stands for "specific absorption rate" basically the amount of radiation a human body will absorb from a cell phone. The lower the rate the less radiation will be absorbed.

There are basically 2 different standards which are :Indian Standard :
The SAR limit for mobile phones used by the public is 1.6 watts/kilogram (W/kg) Averaged over one gram of body tissue.North American Standard :
The SAR limit for mobile phones used by the public is 1.6 watts/kilogram (W/kg) averaged over one gram of body tissue.European Standard :
The SAR limit for mobile phones used by the public is 2.0 watts/kilogram (W/kg) averaged over ten grams of body tissue.Australian Standard :
The SAR limit for mobile phones used by the public is 2.0 watts/kilogram (W/kg) averaged over ten grams of body tissue.Japan Standard :
The SAR limit for mobile phones used by the public is 2.0 watts/kilogram (W/kg) averaged over ten grams of body tissue.Korea Standard :
The SAR limit for mobile phones used by the public is 1.6 watts/kilogram (W/kg) averaged over one gram of body tissue.New Zealand Standard :
The SAR limit for mobile phones used by the public is 2.0 watts/kilogram (W/kg) averaged over ten grams of body tissueSri Lanka Standard :
Federal Communication Commission (FCC) of United States recommends the SAR limit of 1.6 W / kg in 1 g of tissue (the ICNIRP recommendation may suite for Sri Lanka, as the mobile communication services are based on European technologies).Bangladesh Standard :
The SAR limit for mobile phones used by the public is 2.0 watts/kilogram (W/kg) averaged over ten grams of body tissue.Nepal Standard :
The SAR limit for mobile phones used by the public is 1.6 watts/kilogram (W/kg) averaged over one gram of body tissue.

In order to compare relative radiation of different mobile phones, you can only compare phones using the same standard of measurement.